This invention relates to a novel process for preparing sulfonylurea compounds by contacting a sulfonyl halide with an ammonium, phosphonium, sulfonium, or an alkali metal cyanate salt in the presence of an amine. The term "sulfonylurea" is used broadly herein to refer to a compound containing the sulfonylurea bridge, --SO.sub.2 NHCON--. Sulfonylureas prepared according to this invention are known to possess varying types of biological activity. For example, many are useful as anti-diabetic agents. See, for example, French Pat. No. 1,468,747 (1967); Wojciechowski, Acta Pol. Pharm. 19, No. 2:121-25 (1962); or Logemann et al., Farmaco Ed. Sci. 12, No. 7:586-93 (1957). A wide scope of sulfonylurea compounds has also been shown to possess herbicidal and plant growth regulant activity. A multitude of structural variations exist within this class of herbicides. See, for example, the compounds disclosed in U.S. Pat. Nos. 4,169,719, 4,127,405, 4,120,691, 4,221,585, 4,190,432, 4,225,337, 4,371,391, 4,339,266, 4,191,553, 4,305,884, 4,214,890, 4,339,267, 4,302,241, 4,342,587, 4,310,346, 4,293,330, 4,301,286, 4,370,479, 4,370,480, 4,368,067, 4,369,320, 4,348,219, 3,348,220, 4,333,760, 4,368,069, 4,394,506, 4,383,113, and 4,323,611 as well as European Patent Application No. 7,687, published Feb. 6, 1980, (EP-A) No. 44,212, published Jan. 20, 1982, (EP-A) No. 44,807, published Jan. 27, 1982, (EP-A) No. 44,808, published Jan. 27, 1982, (EP-A) No. 44,809, published Jan. 27, 1982, and (EP-A) No. 99,339, published Jan. 25, 1984, as well as South African Patent Application 838,416.
Sulfonylureas have, heretofore, been prepared by several synthetic methods. The most common method involves the reaction of an appropriate amine with a sulfonyl isocyanate as taught in U.S. Pat. No. 4,127,405. The necessary sulfonyl isocyanate can be prepared by several methods. This may be accomplished by reacting the corresponding sulfonamide with phosgene at reflux in a solvent such as chlorobenzene or xylene, according to the procedure of H. Ulrich and A. A. Y. Sayigh in New Methods of Preparative Organic Chemistry, Vol. VI, p. 223-241, Academic Press, New York and London, W. Foerst, Ed., or by the methods taught in U.S. Pat. No. 4,127,405 (1978), U.S. Pat. No. 4,238,671 (1980), and European Pat. No. 23,141. This method, however, has the disadvantage of requiring high reaction temperature, facilities for handling highly toxic phosgene, and special equipment for the recovery and/or scrubbing of the phosgene/HCl off-gas. The sulfonamide used in this phosgenation process can be prepared from ammonium hydroxide and a sulfonyl chloride as widely reported in the literature, e.g. Crossley et al., J. Am. Chem. Soc. 60, 2223 (1938 ).
Sulfonyl isocyanates have also been prepared by the reaction of sulfonyl chlorides with cyanate salts in the presence of nitrobenzene at 200.degree. C. as taught in W. Guenter Z. Chem., 9, 305 (1969). U.S. Pat. No. 2,974,164 to Franz discloses a similar process for preparing p-toluenesulfonyl isocyanate requiring temperatures of 150.degree.-250.degree. C. and a highly polar solvent such as nitrobenzene. The high temperature required for this reaction makes it unsuitable for many substituted sulfonyl isocyanates due to the instability of these isocyanates at high temperatures.
Japanese Patent Application 51-26816 discloses the preparation of alkyl and aryl sulfonyl isocyanates by the reaction of sulfonyl chlorides with cyanate salts in acetonitrile in the presence of phosphorous pentoxide and one or more catalysts such as lithium iodide, copper(II)bromide, and quaternary ammonium salts.
Another known method for preparing sulfonylureas involves reaction of an amine with a carbamate, e.g. N-(benzenesulfonyl)phenyl carbamate, as taught in European Patent Application No. 44,807.
Due to the problems inherent in the processes described above for preparing sulfonylureas or the sulfonyl isocyanates used as intermediates in preparing sulfonylureas, and due to the increasingly important role played by sulfonylurea compounds as potent and environmentally safe herbicides and plant growth regulants, there is a clear need for new and economical processes for preparing these valuable compounds.